Please check. Is it what you want to achieve?
Bootstrap 3 with inline-blocks
CodePen •
JSFiddle
/* The heart of the matter */
.testimonial-group > .row {
overflow-x: auto;
white-space: nowrap;
}
.testimonial-group > .row > .col-xs-4 {
display: inline-block;
float: none;
}
/* Decorations */
.col-xs-4 { color: #fff; font-size: 48px; padding-bottom: 20px; padding-top: 18px; text-align: center; }
.col-xs-4:nth-child(3n+1) { background: #c69; }
.col-xs-4:nth-child(3n+2) { background: #9c6; }
.col-xs-4:nth-child(3n+3) { background: #69c; }<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
<div class="container testimonial-group">
<div class="row">
<div class="col-xs-4">1</div><!--
--><div class="col-xs-4">2</div><!--
--><div class="col-xs-4">3</div><!--
--><div class="col-xs-4">4</div><!--
--><div class="col-xs-4">5</div><!--
--><div class="col-xs-4">6</div><!--
--><div class="col-xs-4">7</div><!--
--><div class="col-xs-4">8</div><!--
--><div class="col-xs-4">9</div>
</div>
</div>Bootstrap 4 with flexbox
As commented by Hector, the inline-boxes solution works for Bootstrap 4 too, but requires to add display: block; for .testimonial-group > .row.
But Bartimaeus rightly notes that for Bootstrap 4 this result is more appropriate to achieve with the help of flexbox, adding the style classes provided for this: flex-nowrap and overflow-auto.
/* Decorations */
.col-4 { color: #fff; font-size: 48px; padding-bottom: 20px; padding-top: 18px; text-align: center; }
.col-4:nth-child(3n+1) { background: #c69; }
.col-4:nth-child(3n+2) { background: #9c6; }
.col-4:nth-child(3n+3) { background: #69c; }<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.6.2/css/bootstrap.min.css">
<div class="container">
<div class="row flex-nowrap overflow-auto">
<div class="col-4">1</div>
<div class="col-4">2</div>
<div class="col-4">3</div>
<div class="col-4">4</div>
<div class="col-4">5</div>
<div class="col-4">6</div>
<div class="col-4">7</div>
<div class="col-4">8</div>
<div class="col-4">9</div>
</div>
</div>